325 magnum, lean condition

I'm working on a friends 2000 magnum 325 2 wheel drive. It's been having and issiue with it shutting down on him after a little bit of riding. I went thru and cleaned the carb, fuel tank, and that vacume fuel pump thing. He took it up and down the road, and the exaust was glowing red. Checked the plug and it was lean. The needle was set to the middle setting, i put it all the way down to richen it up, and its still running lean. The machine is all stock. I'm not used to the vacume slide on the carb, and that fuel pump set up, so I'm wondering if there are any common issiues with these machines that go bad that I should check out.